"In your phrasing, you could say that government also "tells people what they can and can't" eat, in the form of the FDA."
"The FDA doesn't tell you what drugs you can and cannot take."
The FDA's actions do effectively stop you from having any source to buy a poisoned cucumber, or homeopathic ibuprofen, or whatever else, where said source is a US corporation. But only because it's going after those corporations. It doesn't care what you do.
(In a world where the FDA did care about such things, we'd probably have "drug tourism" laws the way we have "sex tourism" laws, where you could be prosecuted for drugs you used while abroad.)